Railway track circuit apparatus



Nov. 3, 1936.

P. N. MARTIN RAILWAY TRACK CIRCUIT APPARATUS Filed Aug. 50, 1935 Fig. 7.

2 Sheets-Sheet 1 X Q I? T Y T (In? 20 fillegmom INVENTOR Paul NMamm BY412W HIS A TTORNE Y Bridging Nov. 3, 1936. R MA T 2,059,888

RAILWAY TRACK CIRCUIT APPARATUS Filed Aug. 50, 1933 2 Sheets-Sheet 2 fBridginy BY MW HIS A TTORNE Y Patented Nov. 3, 1936 UNITED STATES PATENTOFFIQE RAILWAY TRACK CIRCUIT APPARATUS Application August 30,

22 Claims.

My invention relates to railway track circuit apparatus, and morespecifically to apparatus for improving the shunting characteristics ofrailway track circuits.

I will describe several forms of apparatus embodying my invention, andwill then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing oneform of apparatus embodying my invention. Figs. 2 to 10, inclusive, arediagrammatic views showing modified forms of the apparatus illustratedin Fig. 1, also embodying my invention.

Similar reference characters refer to similar parts in each of theseveral views.

In the form of track circuit commonly employed for railway signaling,the shunting sensitivity varies over a Wide range, due chiefly tovariations in ballast leakage from rail to rail n and the consequentchanges in the energization of the track relay. That is, when theballast is wet and the resulting leakage high, the track relay energylevel is low, and a train shunt of relatively high resistance is capableof releasing the track relay. However, under dry ballast conditions, thetrack relay energization may become abnormally high, so that difficultymay be experienced in obtaining safe shunting under various operatingconditions. The use of a current- ?9 limiting impedance at the feed endof the track circuit, although helpful, does not of itself providesufficiently close regulation of the track relay energy to be entirelysatisfactory.

For uniform shunting sensitivity, it is desirable to maintain the normaltrack relay energy level, prior to the time when the shunt is applied,as nearly uniform as possible, irrespective of ballast leakage, and itis believed that this result can be accomplished most effectively by theuse of regulating apparatus located at the relay end of the trackcircuit. Apart from the effect of ballast leakage on track relayenergization, there is an additional factor which noticeably decreasesthe maximum shunting sensitivity of a track circuit. This factor resultsfrom the practical limitation to which track relays are subject, namely,that the energization at pickup must be greater than the energization atrelease. Therefore, although improved shunting could be obtained bymaintaining the energization of the track relay at the release value,some sensitivity must be sacrificed in the usual track circuit becausethe energization must be at least sufiicientiy high for pickup of therelay. My invention makes it possible to eliminate partly 01;

1933, Serial No. 687,476

wholly the effect of the spread between the pickup and. release values,as well as to offset the disadvantages due to ballast leakage variation,thus providing increased shunting sensitivity as well as decreasedshunting time.

Referring to Fig. l, I have shown a section of railway track F-G, oneend of which is supplied with rail current from. a suitable source 2,through an adjustable limiting impedance 3. Connected across the railsat the other end. of the section is a track relay A, in the energizingcircult of which is included, at times, a resistor R. Relay A controls apickup circuit for an auxiliary relay B, by means of front contact 6.When relay B is picked up, back contact 5 being open, the short circuitis removed from resistor R, thereby decreasing the energization of relayA.

Let it first be assumed that relay B is used to decrease the sheet ofthe spread between pickup and release values of relay A. Under normalconditions with section F-G unoccupied, both relays A and B will bepicked up. The value of resistor R will be determined by the minimumballast condition, so that the amount of energy which is permitted toremain in relay A will depend to a large extent on the track circuitregu lation. If the regulation is good, so that the rail voltage at therelay end does not vary widely with ballast conditions, resistor R maybe cho sen of such a value as will decrease the energy level in relay Aalmost to the release point. Maximum shunting sensitivity can beobtained with such an adjustment, assuming other factors to remainconstant.

When a train enters section F-G, relay A will release, opening frontcontact A to release relay B. As soon as relay B releases, back contact5 will become closed to shunt out resistor R. Consequently, as soon asthe train leaves the section, the energization of relay A will besufiicient for pickup, and the circuit will be restored to the conditionillustrated. From the foregoing, it will be apparent that by a suitablechoice of the value of resistor R with reference to the release point ofrelay A, the shunting sensitivity of the ordinary track circuit can begreatly improved. As is well known, track relays particularly of thedirect current type, have an appreciable spread between the pickup andthe release energy levels, with the result that the train shunt must besufficiently effective to by-pass the increment of current above therelease point of the relay. Not only does this require a lowerresistance train shunt, but the shunting time is also substantiallyincreased because the relay flux requires a longer time to die down fromthe higher level. A further advantage arising from the use of theresistor R is that the addition of resistance in series with theinductance of relay A results in a much more rapid flux decay, i. e.,lower shunting time, than can be obtained at the same value of currentbut without the series resistance. This result will be understood from aconsideration of the time constant of an inductive circuit havingresistance in series therewith. Practically, the combination of relays Aand B is in many respects the equivalent of a single track relay havingpickup and release values which are substantially the same.

Let it next be assumed that relay B and resistor R are used forimproving track relay voltage regulation. If the impedance of relay B ismade substantially higher than that of relay A, and if the limitingimpedance 3 is so adjusted that with low ballast resistance relay A willjust pick up, then when the ballast dries out and the track voltagesrises, relay B will pick up. The pickup of relay B Will remove theexcess energization from relay A, under the dry ballast condition. Theresistor R must be of sufliciently high value to insure that relay Awill release prior to the release of relay B, otherwise the increasedshunting sensitivity will be sacrificed. Because of the relatively highimpedance of relay B, this relay will have only a slight effect on theoperation of the track circuit under conditions of low ballastresistance. With high ballast resistance, however, when the shuntingsensitivity ordinarily becomes very low, the addition of resistor R inseries with relay A will greatly increase the shunting sensitivity, aswell as decrease the shunting time. Relay A is provided with anadditional contact, such as 20, Which may be used to control circuitsfor signals, or any other traflic governing apparatus.

Referring to Fig. 2, which is identical with Fig. 1 except for theaddition of a second auxiliary relay C in parallel with relay B, theoperation of the apparatus of this figure, in view of the foregoingdescription, will be clear without further explanation. Relay C is ofhigher impedance than relay B, and acts to cut in an additional resistorR by means of back contact 5, when the ballast resistance and theresulting track voltage become sufliciently high for pickup of relay 0.In this manner, track circuits having a large ballast resistancevariation can be operated safely. If desired, relay C can be used merelyas an adjunct to relay B, to permit adding the series resistance in twosmall steps, rather than one large step, thus aiding to maintain theshunting sensitivity more uniform throughout the operating range of therelay combination. It will be apparent that if a sufficient number ofauxiliary relays is used, the shunting sensitivity of the track circuitcan be maintained at a uniformly high value, notwithstanding a variationof track voltage between wide limits.

In Fig. 3, the auxiliary relay B instead of being connected across thetwo rails of the track as in Fig. l, is connected in series with relay ARelay B is a low impedance current relay having the same functions asrelay B in Fig. 1. In explaining the operation of the apparatus, I shallassume that the track circuit current has been adjusted under wetballast conditions to that value which will enable relay A to pick up.Since the pickup current of relay B is considerably higher than thepickup current of relay A relay -relay D in order that relay A B will bedeenergized under the above condition, and the energizing circuit forrelay A will include the back point of contact 8 of relay 3 wire 2|, andthe winding of relay B. As the ballast dries out, the current throughrelay B will increase until a point is reached at which relay B willpick up.

As soon as relay B picks up, resistor R will be connected in series withrelay A over the front point of contact 8 of relay B thus compensatingfor the increase in track voltage. At the same time, front contact 9 ofrelay B will close, connecting resistor R, which replaces the winding ofrelay A into the circuit of relay B in order that relay B may remainenergized even though the current through relay A is substantiallydecreased. Contact 8 of relay B is of the continuity transfer type inorder that the energizing circuit of relay A will not be interruptedduring the pickup of relay B When a train enters the track section,relay A will release first, followed by the release of relay B which, inclosing the back point of contact 8, prepares the low resistance circuitfor pickup of relay A as soon as the train leaves the section.

The operating characteristics of relays A and B should be such thatrelay A will be the first to pick up when a train leaves the section,and the first to release when a train enters the section. Should relay Bpick up ahead of relay A resistor R might prevent the pick-up of relay Aor at least retard the pickup unnecessarily. If relay B were permittedto release ahead of A upon shunting of the track, the shuntingsensitivity would be decreased because of the higher energization ofrelay A under this condition. By energizing relay B over the frontcontact I of relay A a relatively quick release of relay B and one whichis necessarily subsequent to the release of relay A is obtained.

Referring to Fig. 4, the circuit of this figure shows a method forobtaining compensation for the spread between the pickup and releasecurrent values, independently of the compensation for high track voltageunder dry ballast conditions. Separate resistors R and B, respectively,are provided for this purpose. The signal control relay D is a repeaterof the track relay A and is of the slow pickup and slow release type. Byemploying relay D for signal control purposes, it becomes possible touse a highly sensitive track relay A since the mechanical work requiredof relay A is very small.

In explaining the operation of the apparatus of Fig. 4, I shall assumethat under the condition of minimum ballast resistance, the track energyhas 5 been adjusted to a value which is sufficient to pick up relay A itbeing understood that the track voltage required to pick up theauxiliary relay B is substantially higher than that required to pick upthe track relay A When relay A picks up. front contact I I will closeand the repeater relay D will become energized from a suitable currentsource having the terminals X-Y. As soon as relay D picks up, backcontact I 2 will open, thereby opening the branch circuit aroundresistor R so that resistor R will be included in the energizing circuitof relay A to compensate for the spread between pickup and releasecurrent values. A time interval is introduced into the pickup oi willreach its fully energized condition before the energization is decreased through the opening of back contact 42. Should contact l2 bepermitted to open before the armature of relay A will have reached itsfully closed condition, an undesired release of relay A ill) mightoccur, with resulting pumping action between the two relays A and D.This difliculty would be particularly prominent under wet ballastconditions, when the track relay energization is low. Another reason forretarding the pickup of relay D is to prevent a momentary clear signalfrom being displayed, should relay A pick up momentarily due to atemporary loss of shunt. The slow release characteristic of relay Dmerely introduces an additional time delay before a change of signalindication may occur, thus providing more time within which a lowresistance shunt can be established when the shunting 1s intermittentlypoor.

When the ballast becomes dry and the track voltage rises, relay B willpick up, opening the branch circuit around resistor R to add thisresistor also, in series with relay A When a train enters the tracksection, relay A will release first, followed by relays B and D.Thereupon, both resistors R and R will be short-circuited, inpreparation for the pickup of relay A as soon as the train leaves thesection.

Referring to Fig. 5, the apparatus of this figure operates in the samemanner as the apparatus of Fig. 4. The normal energizing circuit ofrelay A does not include a front contact of relay A as this contact canbe eliminated if relay D is of the nonslow release type. Relay D shouldpreferably have a slow pickup characteristic, for the same reasonsadvanced in connection with relay D of Fig. 4.

In the modified form of apparatus shown in Fig. 6, the shuntingsensitivity of relay A is increased and the shunting time decrease-d notonly by adding resistance in series with the relay winding, but also bydecreasing the effective turns of the Winding. The operation is asfollows: When the ballast is wet, relay A will be energized and relay Bdeenergized, so that the circuit of relay A will include both windingsi3 and M of the relay, and the back point of the continuity transfercontact 15. If the track voltage increases sufficiently to pick up relay8*.

7 the circuit of relay A will include only portion I3 of the relaywin-ding, resistor R and the front point of contact if) of relay B. Byproperly proportioning the number of turns which are cut out and thevalue of resistor R with respect to the track voltage at which relay Bpicks up, the release characteristic of relay A may be raisedsufficiently, under the dry ballast condition, to make the shuntingsensitivity fully as satisfactory as under the wet ballast condition.The shunting time will, in addition, be much lower with dry ballastbecause the flux decay will be accelerated due to decreased inductanceas well as increased resistance of the circuit. If it is desired toeliminate the bridging feature of contact if, this may be done byplacing a permanent connection around the front point of contact l5,without affecting the operation of the circuit in a substantial manner.

Referring to Fig. l, the circuit of this figure represents amodification of the circuit of Fig. 4,

the chief difierence being that the auxiliary re lay B is controlled bythe track repeater relay D instead of being controlled by the trackrelay directly. When the track relay controls the auxiliary relaydirectly, as soon as the track relay picks up and before it has attainedits fully energized condition, the auxiliary relay comes connectedacross the track, and if the ballast is wet, the added load may besuificient to cause the track relay to release, unless a compensatingadjustment of the current-limiting impedance at the feed end of thetrack circuit is made. Some sacrifice of shunting sensitivity resultsfrom such an adjustment. By controlling relay B over the front point ofcontact iii of relay D relay D being preferably of the slow-pickup type,relay A has ample time within which to reach its fully closed condition,before the current of relay B is added to the track circuit load, sothat ordinarily, the adjustment of the track impedance can remain thesame as though relay B were not used.

The arrangement shown in Fig. 8 is similar to Fig. 1, except that a timedelay relay T of any suitable type, is added to insure that once thetrack relay A has released, it wil remain deenergized until such time,at least, as is required for relay T to complete its pickup movement. Inthis manner undesired changes of signal indication arising frommomentary loss of shunt are prevented. When relay A releases, relay Tbecomes energized over back contact i1, and closes its front contact l8,to close the energizing path for relay A around the open front contactIS.

The apparatus of Fig. 9 is similar to that of Fig. 3, differing chieflyin that the relay B of Fig. 9 is controlled over a back contact of thetrack relay A rather than a front contact of this relay. Relay B isdesigned to have a higherpickup value than relay A In operation, thetrack circuit is so adjusted that relay A will just pick up under themost unfavorable ballast condition. When the ballast resistanceincreases sufliciently, relay B will pick up over a circuit whichincludes the winding of relay A and the back point of contact 22. Theopening of the back point of contact 22 will cause resistor R to beinserted in series with relay A and the closing of the front point ofthis contact will connect resistor R in parallel with relay A thusreducing the energization to increase the shunting sensitivity.

Relay A is designed to release ahead of relay B so that when the trackis shunted, relay A will release, and in closing back contact ll willshort-circuit relay B causing it to release also. With relay B released,the pickup circuit for relay A is restored, so that the track relay willpick up as soon as the train leaves the section.

Referring to Fig. 10, the apparatus of this figure is similar to that ofFig. 9, differing chiefly in that the relay A has a tapped coil, forreasons brought out more fully in the description of Fig. 6. The pickupcircuit for relay A includes both of the relay windings l3 and I4, backpoint of contact l5, and the winding of relay B The track circuit is soadjusted that relay A will just pick up under the most unfavorableballast condition. Relay B having a substantially pickup value, willremain released under this condition. When the ballast dries out, relayB will pick up, opening the circuit for winding M at the back point ofcontact l5, and inserting resistor R in series with winding it by virtueof the closin of the front point of contact l5.

In order to prevent relay A from releasing during the pickup interval ofrelay B contact 15 is made of the continuity transfer type. If it isdesired to eliminate the bridging feature of contact [5, this may bedone by placing a permanent connection around the front point of contact[5 so that the holding circuit for relay A will always be closed,irrespective of whether the pickup circuit is or is not closed at theback point of contact IS. The operation under this condition will be thesame as described above.

When a train enters the section, relay A will release ahead of relay Bclosing back contact 23 which short circuits relay B As soon as relay Breleases, relay A will have its pickup circuit restored through theclosing of the back point of contact 15, in readiness for the pickupoperation as soon as the train leaves the section.

Although direct current track circuits and direct current relays havebeen illustrated for simplicity, it will be apparent that thefundamental principles of connecting one or more impedances after pickupof the track relay, or altering the number of turns, or both, as a meansfor increasing the shunting sensitivity and decreasing the shuntingtime, can be applied as well to track circuits of the alternatingcurrent type, or those employing any other suitable form of electricalenergy.

Although I have herein shown and described only a few forms of apparatusembodying my invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of my invention.

Having thus described my invention, What I claim is:

1. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a track relay and anauxiliary relay, a pickup circuit for said track relay connected acrossthe rails of said section and including a back contact of said auxiliaryrelay, a circuit for said auxiliary relay connected across the rails ofsaid section and including a front contact of said track relay, and animpedance connected across said back contact for decreasing theenergization of said track relay to improve the shunting sensitivity ofsaid track section.

2. The method of increasing the shunting sensitivity of a railway trackcircuit, which comprises connecting a track relay and an auxiliaryr-..ay in such manner that both receive energy over the rails of thetrack circuit, said auxiliary relay having a pick-up value of trackvoltage higher than that required for pickup of said track relay, andusing said auxiliary relay when picked up to decrease the energizationof the track relay by means of a normally ineffective impedance whichbecomes effective when and only when said auxiliary relay is picked upthere-- by rendering said track circuit more sensitive to shunting.

The method of increasing the shunting sensitivity of a railway trackcircuit and decreasing the shunting time, which comprises connecting atrack relay and an auxiliary relay in such manner that both receiveenergy over the rails of the track circuit, said auxiliary relay havinga pick-up value of track voltage higher than that required for pickup ofsaid track relay, and using said auxiliary relay when picked up to add aresistor in series with said track relay to decrease the energizationthereof and to accelerate the flux decay in the core thereof, saidresistor being normally ineffective and becoming effective when and onlywhen said auxiliary relay is picked up.

4. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a track relay and anauxiliary relay, a pickup circuit for said track relay connected acrossthe rails of said section and including a back contact of said auxiliaryrelay, a branch path around said track contact including a resistor, anda circuit for said auxiliary relay connected across the rails of saidsection and including a front contact of said track relay.

5. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a track relay and anauxiliary relay, a pickup circuit for said track relay connected acrossthe rails of said section and including the winding and a back contactof said auxiliary relay, a. holding circuit for said track relayconnected across the rails of said section and including a front contactof said auxiliary relay, and a circuit for said auxiliary relayincluding a second front contact thereof and a front contact of saidtrack relay.

6. In combination with a section of railway track and source of currentconnected across the rails of said section, a track relay and anauxiliary relay, a pickup circuit for said track relay connected acrossthe rails of said section and including the winding and a back contactof said auxiliary relay, a holding circuit for said track relayconnected across the rails of said section and including a front contactof said auxiliary relay and an impedance for decreasing the energizationof said track relay; and a circuit for said auxiliary relay including asecond front contact thereof, a front contact of said track relay, and asecond impedance of substantially the same magniture as the impedance ofsaid track relay.

'7. In combination with a section of railway track and a source ofcurrent connected across the rails of said section; a track relay, anauxiliary relay, and a slow pickup track repeater relay; a pickupcircuit for said track relay connected across the rails of said sectionand including a. back contact of said repeater relay as well as a backcontact of said auxiliary relay, a first branch path around said backcontact of the repeaterrelay including a front contact of the trackrelay and an impedance, a second branch path around said back contact ofthe auxiliary relay including a second impedance, a holding circuit forsaid track relay connected across the rails of said section andincluding said first branch path, a circuit for said repeater relayincluding a second front contact of said track relay, and a circuit forsaid auxiliary relay including a third front contact of said trackrelay.

8. In combination with a section of railway track and a source ofcurrent connected across the rails of said section; a track relay, anauxiliary relay, and a slow pickup track repeater relay; a pickupcircuit for said track relay connected across the rails of said sectionand including a back contact of said repeater relay as well as a backcontact of said auxiliary relay, a. first branch path around said backcontact of the repeater relay including a front contact of the trackrelay and an impedance, a second branch path around said back contact ofthe auxiliary relay includingasecondimpedance. a holding circuit forsaid track relay connected across the rails of said section andincluding said first branch path, a locally energized circuit for saidrepeater relay including a second front contact of said track relay, anda circuit for said auxiliary relay connected across the rails of saidsection and including a third front contact of said track relay.

9. In combination with a section of railway track and a source ofcurrent connected across the rails of said section; a track relay, anauxiliary relay, and a slow pickup track repeater relay; a pickupcircuit for said track relay connected across the rails of said sectionand including a back contact of said repeater relay as well as a backcontact of said auxiliary relay, a first branch path around said backcontact of the repeater relay including an impedance, a second branchpath around said back contact of the auxiliary relay including a secondimpedance, a holding circuit for said track relay connected across therails of said section and including said first branch path, a circuitfor said repeater relay including a front contact of said track relay,and a circuit for said auxiliary relay including a second front contactof said track relay.

10. In combination with a section of railway track and a source ofcurrent connected across the rails of said section; a track relay, anauxiliary relay, and a slow pickup track repeater relay; a pickupcircuit for said track relay connected across the rails of said sectionand including a back contact of said repeater relay as well as a backcontact of said auxiliary relay, a first branch path around said backcontact of the repeater relay including a resistor, a second branch patharound said back contact of the auxiliary relay including a secondresistor, a holding circuit for said track relay connected across therails of said section and including said first branch path, a locallyenergized circuit for said repeater relay including a front contact ofsaid track relay, and a circuit for said auxiliary relay connectedacross the rails of said section and including a second front contact ofsaid track relay.

11. In combination with a section of railway track and a source ofcurrent connected across the rails of said section; a track relay, anauxiliary relay, and a track repeater relay; a pickup circuit for saidtrack relay connected across the rails of said section and including aback contact of said repeater relay, a holding circuit for said trackrelay connected across the rails of said section and including a frontcontact of. the track relay as well as a back contact of the auxiliaryrelay, a branch path around said back contact of the auxiliary relayincluding an impedance, a circuit for said repeater relay including asecond front contact of said track relay, and a circuit for saidauxiliary relay including a front contact of said repeater relay.

12. In combination with a section of railway track and a source ofcurrent connected across the rails of said section; a track relay, anauxiliary relay, and a track repeater relay; a pickup circuit for saidtrack relay connected across the rails of said section and including aback contact of said repeater relay; a holding circuit for said trackrelay connected across the rails of said section and including a frontcontact of the track relay, an impedance, and a back contact of, saidauxiliary relay; a branch path around said back contact of the auxiliaryrelay including a second impedance, a circuit for said repeater relayincluding a second front contact of, said track relay, and a circuit forsaid auxiliary relay including a front contact of said repeater relay.

13. In combination with a section of railway track and a. source ofcurrent connected across the rails of said section; a track relay, anauxiliary relay, and a track repeater relay; a pickup circuit for saidtrack relay connected across the rails of. said section and including aback contact of said repeater relay; a holding circuit for said trackrelay connected across the rails of said section and including a frontcontact of the track relay, a resistor, and a back contact of saidauxiliary relay; a branch path around said back contact of the auxiliaryrelay including a second resistor, a locally energized circuit for saidrepeater relay including a second front contact of said track relay, anda circuit for said auxiliary relay connected across the rails of. saidsection and including a front contact of said repeater relay.

14. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a track relay, apickup circuit for said track relay connected across the rails of saidsection, an auxiliary relay which requires a higher track voltage forpickup than said track relay, a pickup circuit for said auxiliary relayincluding the rails of said section and effective only when said trackrelay is picked up, and normally ineffective means governed by a contactof said auxiliary relay and effective when the auxiliary relay is pickedup for decreasing the energization of said track relay to increase theshunting sensitivity of said track section.

15. In combination with a section of railway track and a source ofcurrent connected across the rails of said section; a track relay and anauxiliary relay both energized from said source over the rails of saidsection, the energization of said auxiliary relay occurring only if saidtrack relay is picked up, said auxiliary relay having a pickup trackvoltage characteristic higher than the pickup track voltagecharacteristic of said track relay; and normally ineffective meansgoverned by said auxiliary relay and effective when and only when theauxiliary relay is picked up for raising the release characteristic of,said track relay to increase the shunting sensitivity of said tracksection.

16. In combination with a section of railway track and a source ofcurrent connected across the rails of said section; a track relay and anauxiliary relay both energized from said source over the rails of saidsection, the energization of said auxiliary relay occurring only if saidtrack relay is picked up, said auxiliary relay having a pickup trackVoltage characteristic higher than the pickup track voltagecharacteristic of said track relay; and normally ineffective meansgoverned by said auxiliary relay and effective when and only when theauxiliary relay is picked up for decreasing the time constant of saidtrack relay to accelerate the flux decay therein, thereby decreasing thetime required to shunt said track relay.

17. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a track relay and anauxiliary relay, a pickup circuit for said track relay connected acrossthe rails of said section and including the winding and a back contactof said auxiliary relay, means controlled by said track relay forreleasing said auxiliary relay when the track relay is released, andmeans controlled by said auxiliary relay effective when the auxiliaryrelay is energized for decreasing the energization of the track relay toimprovev the shunting sensitivity of said track section.

18. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a track relay and anauxiliary relay having a given pickup value which is higher than thepickup value of said track relay, a pickup circuit for said track relayconnected across the rails of said section and including the Winding anda back contact of said auxiliary relay, said pickup circuit serving alsoto pick up said auxiliary relay when the track voltage is at or abovesaid given value, means controlled by said auxiliary relay effectivewhen the auxiliary relay is picked up for decreasing the energiaationand increasing the rate of flux decay in the core of said track relay,and means controlled by said track relay effective when said track relayis released for releasing said auxiliary relay.

19. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a track relay and anauxiliary relay both receiving: current from said source over the railsof said track, and normally ineficctive means controlled by a contact ofsaid auxiliary relay and effective upon the pick-up of the auxiliaryrelay for decreasing the energization of said track relay to improve thetrack shunting sensitivity.

20. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a traclr relay andan auxiliary relay both receiving current from said source over therails of said track, a normally ineffective resistor, and meanscontrolled by a. contact of said auxiliary relay and effective upon thepick-up of the auxiliary relay for adding said resistor in series withsaid track relay to decrease the energization thereof and to acceleratethe flux decay in the core thereof.

21. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a track relay and anauxiliary relay both receiving current from said source over the railsof said track, and normally ineffective means effective only upon thepickup of said auxiliary relay for increasing the track voltage value atwhich said track relay will release.

22. In combination with a section of railway track and a source ofcurrent connected across the rails of said section, a track relay and anauxiliary relay both receiving current from said source over the railsof said track, a normally ineffective impedance, and means eflectiveonly upon the pickup of said auxiliary relay for conmeeting saidimpedance in series with said track relay to thereby decrease the trackrelay energication and improve the track shunting scnsitivity.

PAUL N. MARTIN.

